The invention relates generally to wheelchairs of the type used for self-locomotion and more particularly to an improved wheelchair frame structure which is both resilient and lightweight.
The various needs and requirements of wheelchair users have resulted in a variety of styles and types of wheelchairs. The need for portability has led to numerous types of folding or collapsable wheelchairs, for example. Institutional chairs are usually heavily constructed and have wheel placements which inhibit overturning. "Sports" wheelchairs for racing, basketball and other events are designed for lightness, impact resistance, agility or other specific qualities related to their use.
Despite the variety of wheelchair designs and types, it is possible to generally catagorize certain principals of prior art wheelchair construction. Wheel placement largely determines stability, for example. Virtually all wheelchairs have been designed with the large rear drive wheels placed near the back of the chair, well behind the center of gravity, to inhibit a backward rollover by the occupant. Frames are constructed with vertical struts to transmit weight from the seat to the wheel axles. If weight is to be saved, it is usually accomplished by using lightweight metals such as aluminum. Impact resistance is achieved by reinforcement of the frame. Finally, most prior art chairs have numerous adjustments which permit the wheels and other parts to be selectively shifted relative to the frame.
Following these principals of wheelchair design, it has not heretofore been possible to arrive at a satisfactory combination of lightness, resilience, and portability together with superior agility. The problem is that the factors which promote one desirable feature generally inhibit others. Ultralight metals usually have less strength, for example, and require additional struts and other structural reinforcement. Struts, or vertical members, in turn, transmit shock from the wheels to the seat and other parts, reducing comfort and creating the need for additional reinforcement. Making a wheelchair collapsible adds considerable weight which is inconvenient for handling and transport. Similarly, provision for wheel and other adjustments adds weight. The positioning of the drive wheels for maximum stability tends to inhibit agility, making it difficult or impossible for a user to climb curbs or otherwise maneuver the wheelchair.
There is consequently a need in the wheelchair industry for an improved wheelchair. In particular, there is a need for a wheelchair which combines agility, as found in "sports" models, with exceptional lightness. There is also a need for a wheelchair in which strength and resilience are present in a frame having a minimum number of structural members. There is also a need for a wheelchair which is both conveniently portable and adaptable to specific user needs without a large amount of weight-adding hardware.